Image reading system using an interruption of a pulse train to adjust a scanning period

ABSTRACT

An image reading system including a charge storing type image sensor drives a manuscript or an image sensor in accordance with a driving pulse from a driving unit. A speed of the driving pulse from the driving unit is determined by a speed setting unit, depending on a change of a period of the apparatus scan. The driving pulse is stopped for a certain period of time, so that the difference in a speed of the driving pulse between the different apparatus scan periods is decreased.

This is a divisional of Pat. No. 5,278,675 issued Jan. 11, 1994, nowU.S. Pat. No. 5,278,675, which is a continuation application of Ser. No.07/442,873 filed on Nov. 29, 1989, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an image reading system such as afacsimile, and more particularly to an image reading system using acharge storing type image sensor to minimize a reading distortion.

Recently demand has been increasing for a low-cost, miniaturized imagereading apparatus such as an image scanner and a facsimile, and also fora low-cost, miniaturized image sensor and motor to be used with such animage reading apparatus.

To meet this demand, a contact-type image sensor has been developed inplace of a CCD. The reading period has thus been increased from 2ms/line in a CCD scanner to, for example, 5 ms/line or 10 ms/line, andthus, the reading speed/line has been slowed down. The line means a mainscanning line, called "line" hereinafter. The contact-type image sensoris a charge-storing-type image sensor which stores a predeterminedamount of charge subjected to an optical electrical conversion in apredetermined period. Therefore, the amount of charge stored varies withthe period. Thus, it is necessary to perform a scanning within apredetermined period.

To meet the low-cost requirement for the motor, a motor with a lowresponse characteristic and low positional accuracy is adopted.Therefore, the reading position of the contact-type image sensor isshifted by a large amount.

In a conventional facsimile, a manuscript paper starts from a stoppedstate, increases its speed to a maximum and then decreases its speeduntil it stops. This is conducted in accordance with a motor controlbased on the amount of data which can be transmitted in one line.

For a more detailed explanation, the facsimile determines, based ontraining before a transmission of image data whether the data of thecurrently used line can be transmitted, for example, at 9600 bit/sec. Ifit cannot be transmitted at 9600 bit/sec, the facsimile furtherdetermines whether it can be transmitted at 7200 bit/sec. In accordancewith such training, data is transmitted selectively at various speedssuch as: 14000 bit/sec, 9600 bit/sec, 7200 bit/sec, 4800 bit/sec and2400 bit/sec. The speed at which a manuscript paper to be transmitted isread should be variable. Thus, in a facsimile, the image data which hasbeen read is compressed, the compression ratio varying depending on thekind of image. Furthermore, the transmission speed is not constantduring reading. To prevent the buffer for storing the transmission datafrom being empty, and to prevent the buffer from overflowing, the speedat which the paper is transmitted should be controlled. Therefore, astepping motor, for example, can be used to control the period of thedriving pulse. An image sensor of a reading apparatus or a manuscriptpaper is moved a predetermined distance in the sub-scanning direction ateach driving pulse.

Conventionally, the speed control of the image sensor or the manuscriptpaper is performed within a period given by an integer times the periodfor reading by an image sensor. However, when the reading period of animage sensor becomes slow, such as 5 ms/line or 10 ms/line as statedabove, the reading position shift of the image sensor cannot bedisregarded.

The manuscript shown in FIG. 1A is moved under the condition that areading time period by the image sensor is at 10 ms/line scan, the pulserate required for the stepping motor is 4 pulses/line, the sub-scanningline density is 7.7 lines/mm and the scanning speed of the readingapparatus (i.e. a reading cycle of the data on one main scanning line)is changed from 20 ms/line scan to 10 ms/line scan, for example. Asrecited above, the scanning speed of the reading apparatus (which isdetermined by the relative speed between the manuscript paper and theimage sensor and is called an apparatus scan hereinafter) varies withthe amount of data stored within a memory in which reading data in thereading apparatus is stored and the state of a line to which a facsimileapparatus is connected.

The reading of the pattern shown in FIG. 1A is described with regard tolines l1 to l7. The apparatus scan is at a speed of 20 ms/line fromlines l1 to l3 and is at 10 ms/line between lines l3 and l7 (i.e. thespeed of the apparatus scan is changed at line l3 to a high speed), therotation speed of the motor cannot be immediately changed to 10 ms/line.As a result the positions of lines l4 and l5 are delayed as shown bylines l4' and l5' in FIG. 1B. Thus, when the manuscription speedchanges, the sub-scanning line density of 7.7 lines/mm is not satisfiedand the reading width is narrowed.

The image obtained by this reading operation is reproduced at a rate of7.7 lines/mm. As shown in FIG. 1C, the portion between lines l3 and l5'of the character is extended. When the speed of the apparatus scan isreduced, the situation is reversed.

When the reading time period of the image sensor is at 10 ms/line scan,the pulse rate required for the motor drive is 4 pulses/line, thesub-scanning line density is 7.7 lines/mm, and the scanning speed of thereading apparatus is changed from 80 ms/line to 10 ms/line, then, thereading position of the image shown in FIG. 6A is as shown in FIG. 6B ina prior art apparatus, and reading lines are spaced at equal intervalsin a longitudinal direction in FIG. 6B. As a result, an output isobtained as shown in FIG. 6D.

In the prior art, where an image sensor reads at 10 ms/line scan, thescanning speed of the apparatus is increased from 40 to 30 to 20 to 10ms/line scan. Then, upon a change from 20 to 10 ms/line, a shift inreading position in which a reading is conducted, is 1/154 mm/line, thenthe density of a sub-scanning line is 7.7 line/mm. When the speed of anapparatus scan increases from 30 to 20 ms/line, the shift in positionbecomes 1/30.8 mm/line.

When a motor with a poor transient response characteristic is used, theshift in reading position is caused when the reading position iscontrolled by a motor at the rate of an integer times a period ofreading by an image sensor, thereby decreasing the quality of the imageto be output.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide an imagereading system in which a shift in image reading position upon a readingof an image by a reading apparatus is decreased.

A feature of the present invention resides in an image reading systemcomprising a charge storing type image sensor, a device for driving amanuscript or image sensor, a device for outputting a driving pulse fordriving the driving device, a speed setting device for determining adriving state of said driving device, and a device for providing astopped period of the output of the driving pulse in a predeterminedperiod in an apparatus scan based on the output of the speed settingdevice so that the difference of the driving speed between the differentapparatus scan periods is decreased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are views for explaining a problem of the prior art.

FIGS. 2A to 2E are views for explaining the principle of the presentinvention.

FIG. 3A is a block diagram of an embodiment of the present invention.

FIG. 3B is a block diagram showing the structure of the speed settingunit.

FIGS. 4A and 4B are views for explaining a comparison between thetimings in the prior art and in the present invention.

FIGS. 5A and 5B are views for explaining a shift in a reading positionby comparing the prior art with the present invention.

FIGS. 6A to 6E are views which compare the image data of the prior artwith that of the present invention.

FIG. 7 is a detailed circuit diagram of an embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 2A shows a principle of the present invention which provides animage sensor driving unit 2 for driving a charge- storing-type imagesensor 1, a motor drive control unit 4 for driving a stepping motor 3and a speed determining unit 5 for setting the speed of pulse motor 3.

For example, when the apparatus scan by a reading apparatus using animage sensor whose reading time period is 10 ms, namely, a one-linedata-obtaining cycle, is increased from 20 ms/line to 10 ms/line, cyclesT₁, T₂, T₃ and T₄ of an apparatus scan are executed at 20 ms/line asshown in FIG. 2B. Thus, reading data D2 is not used when the readingdata, for example, initial data D1 only, is made effective. Then, themotor pulse is controlled in the following manner. At cycle T₂ of anapparatus scan, 4 pulses are provided during a period of 17 ms and asupply of pulses is stopped during a period of 3 ms. At cycle T₃, 4pulses are supplied during a period of 14 ms and thus a supply of pulsesis stopped during a period of 6 ms. At cycle T₄, 4 pulses are providedduring a period of 12 ms, thereby stopping a supply of pulses during aperiod of 8 ms.

In this example, stepping motor 3 is subjected to a drive of4-pulses/line. Therefore, a setting of the pulse supply, including astopping period as recited above, is performed by speed setting unit 5and motor drive control unit 4 is controlled by main control unit 7based on a setting signal from speed setting unit 5, thereby producing apulse as stated above and controlling stepping motor 3. Control endjudging unit 6 notifies a control completion within a scan period ofrespective apparatuses.

Therefore, when the manuscript shown in FIG. 2C is read, the readingposition of the image sensor is as shown in FIG. 2D. The reading of thedata is performed twice per line, as stated above, and the formerreading is made to provide effective data. Thus, the resulting imageoutput becomes as shown in FIG. 2E, thereby decreasing the influence ofa shifting of a reading position.

An embodiment of the present invention will be explained by referring toFIGS. 3A to 6E.

FIG. 3A shows the structure of one embodiment of the present invention,FIG. 3B shows the structure of the speed setting unit of thisembodiment, FIGS. 4A and 4B are respectively views for explaining thetiming chart of the prior art and that of the present invention, andFIGS. 5A and 5B are respectively views for explaining a shift of areading position in the prior art and in the present invention.

The same reference numbers are used in FIGS. 2A and 3A to represent thesame portions. The embodiment shown in FIG. 3A comprises gate 10, pulsegenerator 11, motor driving unit 12, motor controlling unit 13, ANDcircuit 14 and latch 15.

Gate 10 is used to select an effective reading data obtained from acharge-storing-type image sensor. For example, as shown in FIG. 4B,where the apparatus scanning speed is increased from 80 ms/line to 10ms/line, and a 10 ms/line scan can be used as an image sensor, and aread data D1, D2 . . . of image sensor 1 are output every 10 ms. Thefirst reading data D1 of the respective apparatus' scan period is madeeffective, as gate 10 is controlled to perform an on-and-off operationin synchronization with a scan period of respective apparatuses.Therefore, an effective data-selecting signal is output from maincontrol unit 7 and effective timing data, as shown in FIG. 4B, is outputfrom gate 10.

Pulse generating unit 11 outputs a motor pulse signal for drivingstepping motor 3 and apparatus scanning is increased from 80 ms/line to10 ms/line as described above. Therefore, a motor pulse signal isoutput, as shown in FIG. 4B. Namely, until the speed of the apparatusscan is increased from 80 to 60 to 40 to 30 ms/line, motor pulses areoutput during the entire data-reading period. During the period from thesecond 30 ms/line to the 10 ms/line, the motor pulses are selectivelylacking, thereby controlling a shift in reading position. Namely, amotor stopping period of 5 ms is provided in period t₅, 3 ms in periodt₇, 6 ms in period t₈ and 8 ms in period t₉.

During the period in which the motor is stopped, four pulses arerequired to drive an image data reader by one line where the scanningspeed or reading period of image sensor 1 is 10 ms and the apparatusscanning period is X ms, 10 ms=X ms/4 pulses and thus X=40 ms.Therefore, the period must be selectively provided during which themotor is stopped to correct the reading position when the apparatus scanperiod is smaller than 40 ms. However, this period is not necessary whenthe apparatus scanning period is more than 40 ms.

Suppose that the reading period of the image sensor is m and one pulseperiod of the motor pulse is n. When n≧m, the motor need not be stopped.However, when n<m, the period during which the motor is stopped shouldbe provided to minimize the speed difference caused by the drive of amotor by the motor pulse.

When a stepping motor with a bad transient characteristic is used, thestepping motor cannot be responsive to a change in rotation speed upon ahigh rotation speed and thus phase delay is produced when the rotationincreases in a stepped manner and a phase advance is generated when itdecreases in a stepped manner. In order to decrease the phase advanceand delay, the reading period is made an integer times the reading speedby the image sensor where the speed of the stepping motor is changed ina stepped manner, for example, 20 ms/line to 10 ms/line, therebychanging the driving pulse of the step motor and stopping its drivingpulse during the period of difference between the 4 driving pulses ofthe step motor and the reading period of the image sensor, thedifference being caused by a change in the rotation speed of the stepmotor in a stepped manner.

As shown in FIG. 3A, pulse generator 11 is provided with a counter. Acount starts when the pulse generating period Tpms is given and a singlepulse signal is produced every time 1/4 Tpms is counted and the endingsignal is produced upon completion of a TP count. Motor driving unit 12produces a motor pulse in accordance with a motor pulse signal suppliedby pulse generator 11.

Motor control unit 13 outputs an initiation signal or end signal andother control signals to pulse generator 11 or motor driving unit 12 inaccordance with a control signal transmitted from main control unit 7comprising a processor. A gate signal is output to AND circuit 14 ofcontrol end judging unit 6 at every fourth pulse-motor signal. A controland judging signal "1" is output when an AND condition of a reading dataD₁ of image sensor 1 at apparatus scan periods t₁, t₂ . . . and everyfourth motor pulse is established. Therefore, control end judgingportion 6 provides latch unit 15 to maintain a falling point of thefirst reading data D1, thereby checking the AND condition. When theoutput of AND circuit 14 is "1", latch unit 15 is reset.

FIG. 3B shows a structural view of speed setting unit 5. Speed settingunit 5 comprises ROM 16 with motor speed setting data table 17,detecting unit 18 for detecting a capacity in which the data is storedin line memory 19, line memory 19 comprising RAM and up/down counter 20for performing up or down functions or maintaining functions.

Next, an operation of the embodiment of the present invention shown inFIG. 3B is explained as an example in which the speed of apparatusscanning increases from 80 to 10 ms/line as shown in FIG. 4B.

(1) Line memory capacitor detecting unit 18 detects the present vacantcapacity in line memory 19 in accordance with an instruction from maincontrol unit 7. Main control unit 7 then performs an up/down ormaintaining operation on counter 20 as a result of the detection of thevacant capacity of line memory 19. Counter 20 outputs the address oftable 17. When the address value represented by the output of counter 20is "0 0", data A corresponds to the address "0 0", namely, the datawhich is a motor pulse signal corresponding to an apparatus scan periodof 80 ms/line and represents the motor pulse generation periodcorresponding to the motor pulse shown in FIG. 4B. It is transmittedfrom ROM 16 to main control unit 7 and output from main control unit 7to motor driving control unit 4. This enables pulse generator 11, whichhas the same structure as the prior art apparatus, to output the motorpulse. Namely, the motor pulse train in which the fourth motor pulsefalls at the end of period t₁ is produced and is transmitted to steppingmotor 3 by motor driving unit 12 to drive stepping motor 3. At a periodt₁, reading data D₁ to D₈ of image sensor 1 are output and initialreading data D₁ is controlled to be output to gate 10 from main controlunit 7. Thus, the effective data is output at a timing shown in FIG. 4B.The falling-edge timing signal of reading data D₁ is transmitted fromimage sensor driving unit 2 to latch unit 15, thereby enabling latchunit 15 to produce "1". At period t₁, a timing signal "1" representing afalling-edge of the fourth motor pulse is output from motor drivingcontrol unit 4 to an AND circuit 14 to turn on. Therefore, a control endjudging unit 6 outputs a control completion signal to main control unit7 and an on signal of AND circuit 14 resets latch unit 15.

(2) Such a control can be conducted sequentially from the periods t₂ tot₄. Namely, when a lack of capacity is continuously recognized by linememory capacity detecting unit 18, counter 20 is incremented to increasethe motor speed, thereby varying the address values "00", "01", "02" and"03". Data A, B, C, D are stored in table 17 in correspondence with theaddress values "00""01""02" and "03" and, based on these values, motordriving control unit 4 varies the rotation of the motor so that it scansfrom 80 ms/line to 30 ms/line.

When main control unit 7 requests a motor pulse signal from speedsetting unit 5 at period t₅, speed setting unit 5 outputs four motorpulse signals, namely, data F of the address 04 in table 17, for thefirst 25 ms of 30 ms period. Therefore, the corresponding motor pulse isoutput from pulse generator 11 and stepping motor 3 completes anoperation during the first 25 ms at the period t₅ responsive to theabove operation and is put in a stopped state for the remaining 5 ms.Timing signal "1" is output from motor driving control unit 4, 25 msafter the start of period t₅, namely, at the time of the fall of afourth motor pulse. Thus AND circuit 14 is turned on, thereby enablingcontrol end judgement unit 6 to output the control completion signal.However, main control unit 7 recognizes that period t₅ has a time widthof 30 ms, and a control at period t₆ starts 5 ms after the control endsignal is transmitted.

(3) At period t₆, the same control as in (1) is conducted. At periods t₇to t₉, the same control as in (2) is conducted. Namely, at period t₇,main control unit 7 outputs four motor pulse signals for an initial 17ms based on the output from speed setting unit 5. Therefore, a similarmotor pulse is output from stepping generator 11 and the pulse motor 3is driven for the initial 17 ms of period t₇ in accordance with theoutput of pulse generator 11 and is put in a stopped state for theremaining 3 ms period. Such operation is conducted in periods t₈ and t₉.Stepping motor 3 operates for the first 14 ms at period t₈ and is put ina stopped state for the remaining 6 ms period. Stepping motor 3 operatesfor the initial 12 ms of period t₉ and is put in a stopped state for theremaining 8 ms period. Only the reading data D₁ is used as an effectivedata for a respective period. Such control can be conducted up to periodt₁₀.

In the prior art, stopped states are not provided as shown in FIG. 4A.Thus, the effective data of the manuscript becomes as shown by thecircles in FIG. 5A, resulting in an inaccurate image output beingproduced because of an existence of shift of the reading position, asstated above.

In contrast, the present invention provides a stopped period as shown inFIG. 4B and the resulting reading area on a manuscript is as shown bythe circles in FIG. 5B. Therefore, as shown in FIGS. 6C and 6E, thepresent invention can greatly decrease the influence of a shift in areading position.

FIG. 7 shows the embodiment of the present invention in more detail.

Control unit 30 controls an entire apparatus such as a facsimileapparatus. When a document is transmitted by a facsimile apparatus, aset of a manuscript to be transmitted is recognized by control unit 30from a signal obtained from a sensor (not shown). When an operatordepresses the transmission key, control unit 30 outputs a readinginstruction to image sensor driving unit 31. In accordance with thisreading instruction, image sensor driving unit 31 starts a drive ofimage sensor 32.

Image sensor 32 is a sensor of a charge-storing-type which reads animage data of one line by driving image sensor driving unit 31 andoutputs one line of dot data in a dot serial manner. This dot serialdata is applied to serial/parallel converting unit 33 to provideparallel data to be applied to image memory 34 as input image data.

The read out parallel data is output in an FIFO structure. Thisembodiment has memory reading address pointer 35 and memory writingaddress pointer 36 which control a reading address and writing addressof image memory 34. When image sensor 32 reads data, a signal indicatinga completion of a one-line reading is output to image sensor and motorcompletion judging unit 37. Image sensor and motor completion judgingunit 37 comprises two input AND gates, (later described). One linemoving completion signal designating a completion of movement by oneline is made to H level and when a one reading completion signal is at Hlevel, H level is output. The H level output of image sensor and motorcompletion judging unit 37 is applied to memory writing address pointer35 to increment the value of the pointer. Memory writing address pointer35 produces an input image data output from image sensor 32 to producean address pointer designating the position at which data should bestored in image memory 34. When input image data is stored in imagememory 34, address generator 38 generates a storing address of imagememory 34 based on an address output from memory writing address point35, thereby making an access to image memory 34. Namely, every time oneline is read, data is stored in image memory 34 and memory writingaddress pointer 35 increments the address point value.

On the other hand, when memory writing address pointer 35 applies an upsignal to effective image line counter (up/down counter) 39, the output(H level) of image sensor and motor completion judging unit 37 isapplied to a count input of effective image line counter 39 through ORgate 40. When an up signal is added to effective image line counter 39,and the H level output signal is applied to effective image line counter39 from image sensor and motor completion judging unit 37 through ORgate 40, effective image line counter 39 increments a count value.

Image memory 34 is a buffer for temporarily storing read out input imagedata and the image data to be transmitted is read out from image memory34 during the period when control unit 30 reads a manuscript by usingthe image sensor. Therefore, control unit 30 adds the image data outputdesignating signal into effective image line counter 39 through memoryreading address pointer 36 and OR gate 40. Memory reading addresspointer 36 designates a reading address pointer of image memory 34 uponreading and address generator 38 generates a reading address based onthe output of address pointer 36, thereby making access to image memory34. Based on this access, image memory 34 outputs read-out image data.Memory reading address pointer 36 applies a down signal to outputeffective image line counter 39, enabling effective image line counter39 to perform one down count. Namely, effective image line counter 39performs an up count every time one line of data is stored in imagememory 34 and performs a down count every time one line data is read outfrom image memory 34. Therefore, the value of effective image linecounter 39 is equal to the number of lines of data stored in imagememory 34. Control unit 30 receives the output of effective image linecounter 39, namely, effective line number data. When data of imagememory 34 overflows if the manuscript is read at the present speed andcontrol unit 30 decreases a movement speed for reading the manuscript toavoid the overflow data in image memory 34. When the number of effectivedata in image memory 34 is relatively small, the speed at which themanuscript is read is increased to avoid the situation in which datadoes not exist in image memory 34. In a modem used for such a facsimileapparatus the data must be transmitted continuously for one manuscriptunit and the reading speed is controlled to avoid a situation in whichthe number of effective lines becomes 0 during the period of reading onetransmission. A control of a reading speed will be explained in moredetail hereinafter.

The output of effective image line counter 39 is applied to speedjudging unit 41. Speed judging unit 41 determines based on the effectiveline number, whether the present speed should be increased, maintainedor decreased. The result of the determination in speed judging unit 41is output to address counter 42 comprising an up/down counter. Theaddress counter 42 has an up input terminal and a down input terminaland speed judging unit 41 applied an instruction signal (H level) to anup input terminal when it determines that an increase in speed isrequired. The instruction signal (H level) which is output based on thesignal from image sensor and motor completion judging unit 37 changesaddress counter 42. When speed judging unit determines that the presentspeed should be reduced, a clock is input to the down count inputterminal of address counter 42 and whether the address counter 42performs an up or down count is determined based on the content of thedata table 43. Address counter 42 changes the count value based on theclock. The count value of address counter 42 is applied to an addressterminal of motor speed data table 43. Motor speed data table 43 outputsthe speed data corresponding to the count value selected from the speeddata previously stored in motor speed data table 43. At this time, speedjudging unit 41 performs a role for setting the address count valuewithin a range of data. It then generates a *STOP signal when imagememory 34 overflows even when a writing is conducted at the lowest speedand stops the reading operation by AND gate 53.

Motor speed data table 43 stores 80, 60, 40, 30, 25, 20, 17, 14, 12, 10in accordance with the addresses 00 to 90 as shown in FIG. 7. Here,values 80, 60, . . . are in msec corresponding to the reading speed ofone line, which is explained above.

The output of motor speed data table 43 is applied to motor pulsegenerator 44 and data setting circuit 45. Then pulse generator 44generates a pulse with a period corresponding to that of motor speeddata table 43, thus enabling a period of the motor pulse to besynchronized with a reading period of image sensor 32. The output ofmotor speed data table 43 is applied to data setting circuit 45 whichstores the data. The data corresponds to the period of the motor pulseand counter 47 is a presettable counter which loads the speed datastored in data setting circuit 45 upon starting the count, therebyperforming a down count. The clock period of oscillator 46 is 1/4 msecand the output of the oscillator is applied to counter 47. The pulse of1/4 the period of the value stored in the data setting circuit 45 isapplied to motor pulse counter 48 and motor driving unit 51 through ANDgate 49 by means of counter 47. At this time, motor pulse counter 48does not count four pulses. Therefore, AND gate 49 is turned on throughinverter 50.

Motor pulse counter 48 is a 1/4 frequency divider which outputs one linemovement completion signal after four clocks are applied to counter 47.As the output of motor pulse counter 48 is applied to AND gate 49through inverter 50, inverter 50 is turned off and thereafter the outputclock from the counter 47 is prevented from being applied to motor pulsecounter 48 or motor driving unit 51. Therefore, until the reset signalis applied, motor pulse counter 48 is put in a stopped state and thiscorresponds to the period necessary for achieving a synchronization witha reading period of image sensor 32.

When motor pulse counter 48 is put in a stopped state in accordance withan above operation, a one line movement completion signal is output.Therefore, when image sensor and motor completion judging unit 37receives a one-line reading completion signal, it output an H levelsignal, which resets motor pulse counter 48. Counter 47 advances thecounting operation and is simultaneously reset by outputs of H levelfrom image sensor and motor completion judging unit 37 and is thereforereturned to its initial state to perform the same operation repeatedly.

The output of counter 47 is applied to motor driving unit 51 through ANDgate 49 to drive stepping motor 52 to advance the phase at every onepulse, thereby controlling the rotation of the motor to move themanuscript, for example.

The above operation is summarized as follows. Motor pulse generator 44produces four pulses based on the value stored in data set circuit 45and provides a stopped period to be synchronized with n times thereading period of image sensor 32.

Motor speed data table 43 previously stores the data corresponding tothe required speed and increases a rotation speed with less phase delayeven if a requirement for speeding up the motor is continuouslyproduced, thereby suppressing a data shift upon reading a manuscript.

In FIG. 4B, the motor does not stop during the stopped period of t₅ tot₉ but the rotation of the motor increases gradually as the period inwhich the driving pulse is produced is short. In the prior art, therotation is changed abruptly, thereby causing a relatively large phasedelay. In the present invention, the rotation of the motor is increasedgradually when it is changed, thereby decreasing the error caused byphase advance or phase delay.

In the embodiment of the present invention, a step motor for four phasesis used but the step motor of the present invention is not limited tothe four phase type. Motor pulse counter 48 formed on an n-digit countercorresponding to n phases of stepping motor 52 can be applied to an nphase pulse motor.

As shown in FIG. 6A, when the transcript is read and output, the readingposition in the prior art is as shown in FIG. 6B. As a result, atranscript output with a distortion is produced, as shown in FIG. 6B. Incontrast, in the present invention, the reading position of the imagesensor is as shown in FIG. 6C and the output is subjected to lessdistortion, as shown in FIG. 6E.

As described above, the phase delay or advance always occurs when arotation speed of the step motor is changed. Generally speaking, theerror in phase is not important when the rate of the speed change isslow. However, if it is necessary to decrease the error caused upon aslow change of the rotation speed, for example, during the period from80 ms to 30 ms/line in FIG. 6B and then a table shown in the aboveembodiment is provided to change the rotation speed at which arelatively small error is caused. For example, as shown in FIG. 6C, therotation speed of the step motor is changed in a sequence of 80 ms, 60ms, 40 ms, 30 ms, 25 ms and 20 ms. The speed of the step motor is notmerely changed from 80 ms/line to 20 ms/line but is determined based onthe content of the table in which the value of the speed for reducingthe error of the phase is provided although the speed of the step motorchanges, thereby enabling the manuscript or the image sensor to be movedwith a high accuracy.

In the above embodiment of the present invention, the control of thepulse motor is conducted by a motor pulse with a period of integer timesthe reading period of the reading data for the period t₁ to t₄, based onthe table content for the period when the change of the pulse motor isrelatively small, and the speed of the pulse motor is changed from 20ms/line to 10 ms/line, based on the table content for the period whenthe change of the rotation speed of the pulse motor is relatively large,and the empty time period time of the pulse is provided during theperiod of t₆ to t₁₀ in FIG. 4B, thereby enabling an accuracy of theapparatus to be further increased as a whole.

The above explanation is related to the case where the apparatusscanning speed is changed from 80 ms/line to 10 ms/line. However, thepresent invention is not limited to this case.

In the present invention, the apparatus for performing up and downcontrol scan can be smoothly conducted without making the speed of theapparatus scan equal to an integer times the reading period of the imagesensor and without making the motor control equal to integer times thereading period.

Therefore, according to the present invention, the accuracy of thereading position of the image sensor and the transmitting position ofthe manuscript can be greatly increased, thereby effectively decreasingthe shift of the reading position.

What is claimed is:
 1. An image reading system comprising:a chargestoring type image sensor; driving means for driving a manuscriptrelative to said image sensor; a driving control means for outputting adriving pulse for driving said driving means; a speed setting means fordetermining a driving state of said driving means, and outputting tosaid driving means a predetermined number of pulses within one scanperiod; and stopping means for stopping the driving pulse for apredetermined time period to vary a reading speed during said one scanperiod based on an output of said speed setting means so that adifference in a driving speed, of the driving pulse, between differentscan periods is decreased.
 2. The image reading system according toclaim 1, whereina plurality of scan periods, which have the same period,are provided during a gradual increase or gradual decrease of the scanperiod, therein gradually decreasing or gradually increasing saidpredetermined time period of stopping said driving pulse within saidplurality of scan periods based on the output of said speed settingunit.